Apparatus for fabricating stretchable electrical circuit

ABSTRACT

Disclosed is an apparatus for fabricating a stretchable electrical circuit, including: a stretching device configured to stretch a mounted stretchable substrate in two different directions; a marking device configured to mark a mark on the stretchable substrate; an image device configured to obtain an image of the stretchable substrate on which a plurality of alignment marks are marked by the marking device; and a control device configured to control the stretching device, the image device, and the marking device. The control device forms a first axis and a second axis using the plurality of alignment marks marked on the image obtained by the image device and marks one point of a surface of the stretchable substrate with coordinates made by the first axis and the second axis using the first axis and the second axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. patent applicationSer. No. 15/594,766 filed on May 15, 2017, which claims priority toKorean Patent Application No. 10-2016-0058723, filed on May 13, 2016,which are all hereby incorporated by reference in their entirety.

BACKGROUND

The present invention relates to a method of fabricating a stretchableelectrical circuit and an apparatus for fabricating a stretchableelectrical circuit.

A conventional stretchable electrical circuit is formed by forming rigidregions, which are harder than a stretchable substrate, on thestretchable substrate, disposing electrical components in the rigidregions, and electrically connecting rigid islands. Processes ofdisposing the electrical components and electrically connecting therigid islands are manually performed by users themselves.

SUMMARY

Even when a uniform tensile force is applied on a stretchable substrate,a stretching degree of the stretchable substrate varies due to variousfactors including a relationship among a layout of rigid regions on thestretchable substrate, hardness of the rigid regions, and thestretchable substrate. Accordingly, processes of electrically wiringrigid regions and disposing active components, passive components, andthe like in the rigid regions cannot be automatically performed.

The present invention is directed to provide a method of automaticallyfabricating a stretchable electrical circuit and an apparatus forautomatically fabricating a stretchable electrical circuit in order tosolve a problem which was not solved by the conventional art, and toprovide a method and device capable of more economically fabricating astretchable electrical circuit.

According to an aspect of the present invention, there is provided amethod of fabricating a stretchable electrical circuit, which includesstretching a stretchable substrate, forming a plurality of alignmentmarks on a surface of the stretchable substrate, forming a first axisextending from a line connecting two alignment marks among the pluralityof alignment marks and a second axis perpendicular to the first axis,marking one point of the surface of the stretched stretchable substratewith coordinates made by the first axis and the second axis, anddisposing electrical components using the coordinates.

According to another aspect of the present invention, there is providedan apparatus for fabricating a stretchable electrical circuit, whichincludes a stretching device configured to stretch a mounted stretchablesubstrate in two different directions, a marking device configured tomark a mark on the stretchable substrate, an image device configured toobtain an image of the stretchable substrate on which a plurality ofalignment marks are marked by the marking device, and a control deviceconfigured to control the stretching device, the image device, and themarking device, wherein the control device forms a first axis and asecond axis using the plurality of alignment marks marked on the imageobtained by the image device and marks one point of a surface of thestretchable substrate with coordinates made by the first axis and thesecond axis using the first axis and the second axis.

According to embodiments of the present invention, a surface of astretched stretchable substrate may be marked with coordinates, andthereby a process of disposing electrical components on the surface ofthe stretched stretchable substrate may be automatically performed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing in detail exemplary embodiments thereof with referenceto the accompanying drawings, in which:

FIG. 1 is a flowchart schematically illustrating a method of fabricatinga stretchable electrical circuit according to an embodiment;

FIG. 2 is a schematic view illustrating a configuration of an apparatusfor fabricating a stretchable electrical circuit according to anembodiment;

FIG. 3 is a schematic view illustrating a marking device;

FIG. 4 is a schematic view illustrating a case in which a stretchablesubstrate mounted on a stretching device stretches in two differentdirections;

FIG. 5 is a schematic view illustrating a plurality of alignment marksformed on a stretched stretchable substrate;

FIG. 6 is a schematic view illustrating a first axis and a second axisformed using alignment marks;

FIGS. 7 and 8 are schematic views illustrating a process of disposingelectrical components using coordinates; and

FIGS. 9 and 10 are pictures illustrating experimental results when lightemitting diodes (LEDs) are mounted on a stretchable substrate andconnected using the method of fabricating a stretchable electricalcircuit and the apparatus for fabricating a stretchable electricalcircuit according to the embodiments.

DETAILED DESCRIPTION

Hereinafter, a method of fabricating a stretchable electrical circuitand an apparatus for fabricating a stretchable electrical circuitaccording to embodiments of the present invention will be described withreference to the accompanying drawings. FIG. 1 is a flowchartschematically illustrating a method of fabricating a stretchableelectrical circuit according to an embodiment, and FIG. 2 is a schematicview illustrating a configuration of an apparatus for fabricating astretchable electrical circuit according to an embodiment. Referring toFIGS. 1 and 2, the method of fabricating a stretchable electricalcircuit according to the embodiment includes stretching a stretchablesubstrate (S100), forming a plurality of alignment marks on a surface ofthe stretchable substrate (S200), forming a first axis extending from aline connecting two alignment marks among the plurality of alignmentmarks and a second axis perpendicular to the first axis (S300), markingone point of the surface of the stretched stretchable substrate withcoordinates made by the first axis and the second axis (S400), anddisposing electrical components using the coordinates (S500).

The apparatus for fabricating a stretchable electrical circuit accordingto the embodiment includes a stretching device 100 configured to stretcha mounted stretchable substrate sub in two different directions, amarking device 200 configured to mark a mark on the stretchablesubstrate sub, an image device 300 configured to obtain an image of thestretchable substrate sub on which the plurality of alignment marks aremarked by the marking device 200, and a control device 400 configured tocontrol the stretching device 100, the image device 300, and the markingdevice 200, wherein the control device 400 forms a first axis and asecond axis using the plurality of alignment marks marked on the imageobtained by the image device 300 and marks one point of the surface ofthe stretchable substrate sub with coordinates made by the first axisand the second axis using the first axis and the second axis.

The stretching device 100 includes a mounting part 110 on which thestretchable substrate sub is positioned and a fixing member 120 whichfixes the stretchable substrate and stretches the stretchable substratein two perpendicular directions with the same force. The marking device200 prints and marks a plurality of alignment marks A1 and A2 andwirings on the stretched substrate. In one embodiment, the markingdevice 200 is a printing device. The marking device 200 may form wiringsusing a transfer printing process of printing wirings on an insulatinglayer with an ink deposited on a mold as shown in FIG. 3A, an inkjetprinting process of forming wirings by spraying an ink through a nozzleas shown in FIG. 3B, or a gravure printing and roll-to-roll printingprocess of printing wirings on an insulating layer with an ink using aroller as shown in FIG. 3C. For example, an ink used in a printingprocess may be a conductive ink including a conductive material.

The image device 300 has a light axis disposed to be perpendicular tothe surface of the stretchable substrate sub, photographs the surface ofthe stretchable substrate sub to obtain an image, and converts theobtained image into electrical signals to provide the electrical signalsto the control device 400. The control device 400 provides theelectrical signals to the stretching device 100, the marking device 200,and the image device 300 and controls the stretching device 100, themarking device 200, and the image device 300. For example, the controldevice 400 may be implemented as a computer or may be implemented as amicro controller.

Hereinafter, an operation of the apparatus for fabricating a stretchableelectrical circuit according to the embodiment and the method offabricating a stretchable electrical circuit will be described withreference to the accompanying drawings. FIG. 4 is a schematic viewillustrating a case in which a stretchable substrate mounted on astretching device stretches in two different directions. Referring toFIGS. 1 to 4, the stretching device 100 stretches the mountedstretchable substrate sub by applying the same tensile force thereonalong two perpendicular axes (S100). Since the stretching device 100applies the same force on the stretchable substrate sub in theperpendicular directions and stretches the stretchable substrate sub, astretchable substrate sub′ on which a tensile force is not applied yetis isotropically stretched by a tensile force provided by the stretchingdevice 100 in the two perpendicular directions.

For example, the stretchable substrate sub may be formed of an elastomerwhich is a polymer material which may extend or be deformed and may berestored to an original form without permanent deformation. For example,the elastomer may include a polymer, a copolymer, a composite material,or a mixture of a polymer and a copolymer. An elastomer layer refers toa layer including at least one elastomer. The elastomer layer may alsoinclude a dopant and a non-elastomer. An elastomer useful for theembodiment may include a thermoplastic elastomer, a styrenic material,an olefenic material, polyolefin, a polyurethane thermoplasticelastomer, polyamide, synthetic rubber, polydimethylsiloxane (PDMS),polybutadiene, polyisobutylene, poly styrene-butadiene-styrene,polyurethane, polychloroprene, or silicone, but the elastomer is notlimited thereto. The elastomer provides an elastomeric stamp useful forthe method according to the embodiment.

In one embodiment, rigid islands R are located on the stretchablesubstrate sub. The rigid islands may be formed by the following process.A sacrificial layer is formed on a rigid substrate. An upper structureand a lower structure of the sacrificial layer may be separated bydissolving the sacrificial layer in a specific solvent. In oneembodiment, the sacrificial layer may be formed of poly vinyl alcohol(PVA).

A support layer is formed on the sacrificial layer and is cured. Forexample, the support layer may be a PDMS layer. A thermoplastic liquidis disposed on the support layer to form a desired rigid island pattern.For example, the thermoplastic liquid is polymethyl methacrylate (PMMA)and is cured to form the rigid islands. In one embodiment, a process offorming a thermoplastic liquid pattern on a support layer may beperformed using a printing method such as an inkjet printing method, agravure printing method, a roll-to-roll printing method, a transferprinting method, or the like as shown in FIG. 3. In another embodiment,a process of forming a thermoplastic liquid pattern on a support layermay be performed using a dispenser apparatus.

Then, a thermal process is performed, a cover layer is formed to have adesired thickness, and then a curing process is performed. In oneembodiment, a thermal process may be an annealing process and may beperformed at 50 to 150° C. In one embodiment, the cover layer may be aPDMS layer. Then, the cover layer is cured, and the sacrificial layer isremoved using a solvent so that the rigid substrate may be separatedfrom the support layer and a stretchable substrate having rigid islandsmay be formed.

Since the rigid islands R are harder than the stretchable substrate sub,deformation degrees of a cross section and a shape thereof are lowerthan a deformation degree of the stretchable substrate sub even when thestretching device 100 applies a tensile force on the rigid islands R.Accordingly, active components, passive components, and a substrate, onwhich active components and passive components are disposed and wired toperform desired functions, may be disposed on the rigid islands R, whichwill be described below, so that an operating reliability may be insuredto perform desired functions without destruction of the activecomponents, the passive components, and the substrate even when stress,which is generated when the stretchable substrate sub is stretched orrestored to an original shape thereof, is applied thereto.

FIG. 5 is a schematic view illustrating a plurality of alignment marksA1 and A2 formed on a stretched stretchable substrate sub. Referring toFIGS. 1, 2, and 5, the control device 400 controls the marking device200 to form the plurality of alignment marks A1 and A2 (S200). Forexample, the control device 400 controls the marking device 200 to formthe plurality of alignment marks A1 and A2 after the stretchablesubstrate sub is stretched. In another example, the control device 400controls the marking device 200 to form the plurality of alignment marksA1 and A2 before the stretchable substrate sub is stretched.

In the embodiment shown in FIG. 5, two alignment marks A1 and A2 may beformed. In another embodiment (not shown), four alignment marks may beformed to be located at vertices of a quadrangle or three alignmentmarks may be formed to be located at three vertices of a quadrangleexcept one vertex thereof. In still another embodiment (not shown), thecontrol device 400 may control the marking device 200 to form five ormore alignment marks.

FIG. 6 is a schematic view illustrating a first axis and a second axisformed using the alignment marks A1 and A2. Referring to FIG. 6, thecontrol device 400 controls the image device 300 to obtain an image of asurface of the stretchable substrate sub on which a plurality ofalignment marks A are formed. In one embodiment, the image device 300photographs the image of the surface of the stretchable substrate sub ata location in a direction of a light axis perpendicular to the surfaceof the stretchable substrate sub. For example, the image device 300 is adigital camera including an optical device, such as a lens and the like,and an image sensor converting an optical image provided by the opticaldevice into an electrical signal. Since an image provided by the imagedevice 300 is photographed at the location in the direction of the lightaxis perpendicular to the surface of the stretchable substrate sub, animage distortion based on a photographed location can be reduced.

The control device 400 receives the image of the surface of thestretchable substrate sub on which the plurality of alignment marks A1and A2 are formed from the image device 300, and forms a first axis x,which is a virtual line extending from a line connecting the twoalignment marks A1 and A2, and a second axis y which is a virtual lineperpendicular to the first axis (S300). The control device 400 forms thefirst axis x and the second axis y by processing the image provided bythe image device 300. As shown in the embodiment, the control device 400may control the marking device 200 to form the plurality of alignmentmarks so that one of the plurality of alignment marks A1 and A2 islocated at a central portion of the stretchable substrate sub, and theformed first axis x and second axis y may have a starting point which isan alignment mark A1 located at the central portion of the stretchablesubstrate. In another embodiment (not shown), one of the plurality ofalignment marks A1 and A2 may be located at a corner of the stretchablesubstrate sub, and the formed first axis x and second axis y may have astarting point which is an alignment mark located at the corner of thestretchable substrate.

In another embodiment (not shown), the control device 400 may controlthe marking device 200 to form three alignment marks A. Among the threealignment marks A, one alignment mark may be a starting point, a firstaxis x may be a line connecting the starting point and another alignmentmark, and a second axis y may be a line connecting the starting pointand the other alignment mark.

FIG. 6 is a schematic view which marks one point of the surface of thestretched stretchable substrate sub with coordinates made by the firstaxis x and the second axis y. Referring to FIG. 6, the control device400 receives an image obtained by the image device 300 and marks onepoint of the surface of the stretchable substrate sub with coordinatesof a coordinate system formed by the first axis x and the second axis y(S400).

In one embodiment, the control device 400 may mark regions of thestretchable substrate sub, which are uniformly divided by the first axisx and the second axis y and stretched, with coordinates of a coordinatesystem formed by the first axis x and the second axis y. The controldevice 400 forms one alignment mark on the surface of the stretchedstretchable substrate sub and then forms another alignment mark to bespaced a predetermined distance d from the one alignment mark.Accordingly, when a proportion of coordinates of another alignment markand the predetermined distance d is considered, a distance between thealignment marks calculated by a coordinate system and an actual distancebetween the alignment marks on the surface of the stretched stretchablesubstrate sub may be calculated.

For example, a distance between a starting point and the center of arigid island R1 whose center is located at coordinates of x1 and y1 iscalculated by the formula of √{square root over (x1²+y1²)} in acoordinate system formed by a first axis x and a second axis y. Further,a distance between the starting point and an alignment mark located atcoordinates of x2 and 0 is x2 (x2>0) in the coordinate system, and anactual distance between the alignment mark and the starting point on thesurface of the stretchable substrate sub is d. Accordingly, an actualdistance dr between the center of the rigid island R1 and the startingpoint on the surface of the stretchable substrate sub is obtained by aproportional relationship of the following Equation 1.

$\begin{matrix}{d_{r} = {d\frac{\sqrt{{x\; 1^{2}} + {y\; 1^{2}}}}{x\; 2}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Accordingly, the control device 400 may correspond a location havingcoordinates made by the first axis x and the second axis y and an actuallocation on the stretchable substrate sub with 1:1. For example, when awiring is made to connect two different points on the substrate sub in astraight line form, the control device 400 may obtain coordinates of thetwo points and may calculate a length of the wiring formed on a surfaceof the stretchable substrate sub and a distance moved by a markingdevice to form the wiring using the coordinates.

In another embodiment, the control device 400 may control the markingdevice 200 to form alignment marks before a stretchable substrate isstretched. The control device 400 may measure and obtain a distancebetween alignment marks using measuring gradations displayed on thestretching device 100 after the stretchable substrate sub is stretched.Further, since the stretching device 100 stretches the stretchablesubstrate sub in perpendicular directions with the same force, thestretchable substrate is uniformly stretched in the perpendiculardirections. Accordingly, an actual distance can be calculated withrespect to an arbitrary location of the surface of the stretchablesubstrate sub on the basis of the distance d between the alignment marksformed along the first axis x.

FIGS. 7 and 8 are schematic views illustrating a process of disposingelectrical components using coordinates. An embodiment of presentinvention is assumed that a conductive wiring, which is an electricalcomponent, is disposed to connect one electrode of a diode D, which isdisposed on a rigid island R1 whose center has coordinates of x1 and y1,and one electrode of a resistor R disposed on a rigid island R2 whosecenter has coordinates of x3 and y3.

FIG. 7 is a schematic view illustrating a process of determininglocations of rigid islands. The control device 400 determines locationsof rigid islands by processing an image of a surface of the stretchablesubstrate sub provided by the image device 300. The control device 400determines that the center of a rigid island R1 has coordinates of x1and y1 and the center of a rigid island R2 has coordinates of x3 and y3,wherein the centers will be wired.

In one embodiment, during a process of determining the locations of therigid islands, coordinates of the centers of the rigid islands, radiiand diameters of the rigid islands, and the like may be determined.Further, a user of a system may directly determine the locations of therigid islands and may input the locations to the control device 400.

Although the embodiments of FIGS. 7 and 8 show examples in which apremade component is disposed on the rigid island R1, a thin filmtransistor (TFT) formed by performing a printing process, a lightemitting component formed by performing a printing process, and acommercial integrated chip (IC) may be disposed on the rigid island inanother embodiment (not shown).

Referring to FIG. 8, the control device 400 obtains coordinates ofelectrodes to be electrically connected to each other and controls themarking device 200 to perform a wiring process of connecting theelectrodes. As described above, the marking device 200 may be a printingdevice, and the marking device may perform a wiring operation byprinting a conductive ink on a surface of a substrate. For example, theconductive ink may be an ink including silver nanoparticles, an inkincluding copper nanoparticles, an ink including gold nanoparticles, andan ink including carbon nano tubes (CNTs).

In one embodiment, a surface of a stretchable substrate may be modifiedto improve adhesion between a conductive material printed by a markingdevice and the surface of the stretchable substrate sub. For example, anapparatus for fabricating a stretchable electrical circuit may furtherinclude a chamber (not shown), and an ultraviolet treatment and/or ozonetreatment may be performed on the surface of the stretchable substratein the chamber to improve adhesion with respect to the conductivematerial.

Although the embodiments of FIGS. 7 and 8 show examples of wiringsbetween the rigid islands using the disposed electrical components, thecontrol device 400 may control an actuator (not shown) to disposeelectrical components, such as a passive component, an active component,and a substrate on which active components and passive components aredisposed and wired to perform desired functions, on desired locations inanother embodiment (not shown).

In one embodiment, the control device 400 obtains coordinates of rigidislands of a substrate and forms a pattern of disposing electricalcomponents on the rigid islands in order that a stretchable electricalcircuit performs desired functions. Then, the control device 400 mayperform a wiring process of electrically connecting the electricalcomponents using the formed pattern.

After the process of disposing the electrical components is completed,the control device 400 controls the stretching device 100 to restore thestretchable substrate sub to an original state thereof. Since the wiringformed on the stretchable substrate sub is formed while the substrate isin a stretched state, the wiring has a creasy form when the stretchablesubstrate sub is restored to the original state. However, even when thestretchable substrate is stretched, the crease formed on the wiring isunfolded and the wiring performs a function of electrical connectionwithout being disconnected. Even when the substrate is stretched orrestored to the original state, deformation of the rigid islands is low.Accordingly, even when the substrate is restored to the original state,deformation, such as crease or the like, does not occur in theelectrical components located at the rigid islands.

EXPERIMENTAL EXAMPLE

An experimental result of disposing and wiring light emitting diodes(LEDs) on a stretchable substrate using the method of fabricating astretchable electrical circuit and the apparatus for fabricating astretchable electrical circuit according to the embodiment will bedescribed with reference to FIGS. 9 and 10. FIG. 9A is a viewillustrating a stretchable substrate having a rigid island R formedthereon and stretched in two perpendicular directions. As shown in FIG.9A, since the same tensile force is provided in the two perpendiculardirections, the stretchable substrate is isotropically stretched.

FIG. 9B is a view illustrating LEDs disposed in a rigid island R. Asdescribed above, a process of disposing electrical components on therigid island R may be performed by an automatic process usingcoordinates.

FIG. 10A is a view illustrating a pattern to be formed with respect toLEDs disposed on a stretchable substrate. A control device obtainscoordinates of each electrode of the LEDs from an image provided by animage device. The control device controls a marking device to desirablyconnect the LEDs using the obtained coordinates. The marking device iscontrolled by the control device and performs wiring using a conductiveink. In the experimental example, the wiring was made by an inkjetprinting process of spraying the conductive ink through a nozzle.

FIG. 10B is a view illustrating a state in which a driving voltage issupplied to a stretchable substrate on which wiring is completed andlight is emitted by LEDs. As shown in FIG. 10B, it was determined thatthe electrical components are disposed at desired locations and driven.

In a conventional case, even when the same tensile force is applied to astretchable substrate on which rigid islands are formed, it is difficultto estimate stretching directions and stretched degrees of thestretchable substrate on the basis of a layout and hardness of the rigidislands and a relationship between the rigid islands and the stretchablesubstrate. Accordingly, it is impossible to automate processes ofdisposing and electrically wiring components on the rigid islands.

However, according to the embodiment, coordinates of regions on asurface of a stretched stretchable substrate can be obtained, andthereby electrical components can be automatically disposed in theregions using the obtained coordinates.

It will be apparent to those skilled in the art that variousmodifications may be made to the above-described exemplary embodimentsof the present invention without departing from the spirit or scope ofthe invention. Thus, it is intended that the present invention coversall such modifications provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An apparatus for fabricating a stretchableelectrical circuit, comprising: a stretching device configured tostretch a mounted stretchable substrate in two different directions; amarking device configured to mark a mark on the stretchable substrate;an image device configured to obtain an image of the stretchablesubstrate on which a plurality of alignment marks are marked by themarking device; and a control device configured to control thestretching device, the image device, and the marking device, wherein thecontrol device forms a first axis and a second axis using the pluralityof alignment marks marked on the image obtained by the image device andmarks one point of a surface of the stretchable substrate withcoordinates made by the first axis and the second axis using the firstaxis and the second axis.
 2. The apparatus according to claim 1, whereinthe control device controls the plurality of alignment marks to bemarked on the stretched stretchable substrate.
 3. The apparatusaccording to claim 1, wherein the control device controls thestretchable substrate to be stretched after the plurality of alignmentmarks are marked.
 4. The apparatus according to claim 1, wherein thestretchable substrate is a substrate on which a rigid island is formed.5. The apparatus according to claim 1, wherein the control device formsthe first axis and the second axis using a distance between twoalignment marks among the plurality of alignment marks marked on thestretched stretchable substrate.
 6. The apparatus according to claim 1,wherein the marking device is a printing device and prints and forms theplurality of alignment marks.
 7. The apparatus according to claim 1,further comprising an arranging device configured to dispose electricalcomponents on the substrate, wherein the electrical component includes apassive component, an active component, and a circuit substrate on whichthe passive component or the active component is disposed.
 8. Theapparatus according to claim 7, wherein the marking device forms wiringsconfigured to connect the electrical components.